Abstract
Major context of international law, namely the territorial regulations, has envisaged a fundamental change since the emerge of nation-states. How to maintain the stability and universality of international law so to be followed at will by both the old and new civilized states then become a core issue for the international judiciaries while interpreting them. It is well noticed that decolonization per se is an instant example of such a drastic evolution of jus gentium. The purpose and outcomes of decolonization allow a gross renewal or renovation of the subject of international society, which together with the revocation of established rules of territorial acquisition made and maintained through the colonial period, forced the insertion of new thinking and imaginaries into the reading of the old rules. Nevertheless, utilities used to compromise the conflicting values among the old and new regulations, such as the doctrine of intertemporal law, is also proved to be indivisible. The Southeastern Asian states share the same colonial history and consequently the culture context, so the territorial disputes among them could help to serve as a natural forum to reveal the practical aspects of systemizing intertemporal law, including the broader interpretation and application of the doctrine. This article is therefore intending to deplore the major elements used to carve out the doctrine in the jurisprudence over the territorial disputes of The Southeastern Asian states, such as ”the critical date”, ”colonial effectivités”, maps and other documentary evidence, and jus cogens, so the substantial aspects, i.e., the applicability and limitation of the doctrine in modern international law may be further analyzed.